In a related art electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charges thereon in irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to informational areas contained within the original document.
After the electrostatic latent images are recorded on the photoconductive member, the latent images are developed by bringing developer material into contact therewith.
The developer material may include toner particles adhering triboelectrically to carrier granules. This two-component developer may be mixed and stored in a developer housing. Typically, individual toner particles are maintained within the developer housing for a relatively short period of time, preferably not exceeding several days.
The toner particles are attracted from the carrier granules to the latent images, forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a recording medium such as, for example, a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet. After each transfer process, the toner remaining on the photoconductive member is cleaned by a cleaning device.
In order to operate effectively, a proper concentration of the toner particles relative to the carrier granules is desirable. Excessive toner concentration within the developer housing can lead to prints that are too dark. Insufficient toner concentration can lead to prints that are too light.
Systems are known that measure toner concentration based on a magnetic permeability of the developer. Generally, carrier granules are magnetically permeable, whereas toner particles are relatively non-magnetic. Thus, toner concentration affects the permeability of the mixture. Lower concentrations of toner particles lead to greater permeability of the mixture and vice-versa.
Various factors, which will be discussed further below, affect the accuracy of sensors that measure toner concentration, such as permeability sensors, thus requiring more refined testing in order to accurately calibrate image forming devices that rely on maintaining consistent levels of toner concentration. Such calibrations may include, for example, the relative rate of toner size or charge distribution within the device.
Other systems are used to measure both toner concentration and charge-to-mass ratio of developer material samples extracted from image forming devices. Toner concentration and charge-to-mass ratio of two-component developers can be measured with an air blow-off or blow-through technique using “tribocages.” In such a technique, a sample of developer material is placed in a metal cylinder with screen ends, e.g. a tribocage. The screens have apertures that are small enough to retain the carrier, but large enough to allow toner from the developer material to pass through. Compressed air is blown through a first screen of the tribocage, stripping the toner particles from the carrier granules and forcing the toner particles through an opposite screen and out of the tribocage.
The change in charge and weight of the tribocage between the beginning of blow-through and end of blow-through is measured, thereby deriving the charge (Q) and mass (M) of the toner particles that have been removed from the tribocage. The mass of the two-component developer sample may be calculated by subtracting the weight of the tribocage (empty) from the measured weight of the sample (pre-blow-through) and the tribocage. The calculated mass of the toner particles may then be divided by the mass of the two-component developer sample to derive TC (toner concentration in %). The charge of toner particles may be divided by the mass of the toner particles to derive charge-to-mass ratio of the toner (Q/M).